Grid-controlled space discharge device



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w. R. AIKEN Filed June 21, 1954 v GRID-CONTROLLED SPACE DISCHARGE DEVICE Dec. 9, 1958 IN V EN TOR. ILLIBM R- MREN BY 1 6. )BTTORNEY 10 K J LT AN E VOLTAGE United States Patent GRID-CONTROLLED SPACE DISGHARGE DEVICE William R. Aiken, Berkeley, Calif., assign'on by mesne assignm'ents, to Kaiser Industries Corporation, a corporation of Nevada ApplicationJnne 21, 1954, Serial No. 437,981

15 Claims. (Cl. 313'-2%) This invention relates to electron space discharge devices and more particularly to gridcontrolled vacuum tubes.

In grid-controlled vacuum tubes, and particularly in such tubes wherein an oxide-coated cathode or the like is employed, various undesirable effects resulting in distorted signal reproduction and short tube life have been encountered, particularly when such tubes are operated at high anode voltages, which effects are caused by evolution of secondary emission ions destroying the emissive efiiciency of such cathodes by ion bombardment. Accordingly, it has been the practice in grid-controlled vacuum tubes primarily designed for high anode voltage operation to resort to more expensive and less eflicient electron emitters for the efiectivecathode surface.

One object of this invention is to provide a method of operation and arrangement of components in a gridcontrolled vacuum tube electrode system whereby ion bombardment of the thermionic emissive cathode is prevented. 7

It is an object of the invention to provide in tubes of the type referred to, an ion channelling zone around the cathode which permits electrons to flow from the cathode to the anode but is effective toprevent bombardment of the cathode by ions evolved from the anode area.

It is afurther object of the present invention to provide an arrangement of-cathode, control grid and anode in a vacuum tube of high anode voltage rating which exhibits sharp grid control characteristics substantially independgrid control characteristics, capable of wide application for powersupply regulation or control signal amplification, particularly at high anode voltages.

Itisa further object of the present invention to materiallyincrease the effective life of thermionic electron emissive surfaces of the oxide type.

In accordance with the basic features of the present invention, the electrode system -of a grid-controlled vacuum tube comprising an oxide-coated cathode or the like is constructed and arranged to provide in effective surrounding'relation therewith a control grid and a space charge zone defined bya surrounding screen grid and a surrounding space charge electrode, each arranged outwardly from the cathode in the order recited. The electrode system additionally provides for arrangement of a high voltage anodein spaced and transverse relation with respect to one end of the cathode, controlgrid and space charge zone, thesystem further having an electrostatic shield'or barrier electrode interposed between the end of the cathode and the adjacent anode portion.

In operation of the electrode system recited, the electron discharge path from the cathode is selectively through the control grid into the space charge zone by attraction of the electrons from the cathode with at least one electrode defining the aforementioned space charge zone ice being maintained .at a relatively positive potential with respect to the cathode. By virture of the shielding electrode between the end of the cathode and the anode portion spaced therefrom, the electron flow from the .cathode is controlled by the space charge zone potential and is substantially unaffected by the anode potential. As a feature of the present invention, however, the shielding electrode between the end of the cathode and a portion of the high voltage anode does not extend completely into the area between the aforementioned space charge zone and the anode portions opposing one end thereof. Accordingly, the extent to which electrons are attracted from the space charge zone to the anode is a function of the anode potential. Stated otherwise, it is an important feature of the present invention that electrons originating from the emissive surfaceof'the cathode see only the acceleratingpotential of the space charge zone, whereas electrons in the space charge zone see only the electrons in-the space charge zone, thereby providing an effective sharp cut-off grid control substantially independent of high anode voltage. It is a further important feature of the present invention that, by virture of the arrangement of the shielding electrode between the adjacent anode portion and the end of the emissive cathode, ions which evolve by secondary emission from the'anode either impinge upon the shieldelectrode or the elements of the electrode system defining the space charge zone or traverse harmlessly through said space charge zone without deleterious bombardment of the emissive cathode.

The above and other features of the present invention are hereinafter described and explained in greater detail with reference to-the accompanying drawing, illustrating the constructional and schematic arrangement of a typical embodiment of the invention, together with a graphical presentation of characteristic grid control accomplished thereby, as follows:

Figure 1 is .a schematic vpresentation of an electron discharge device arranged in accordance with the invention;

Figure 2 is a perspectiveview of said electron discharge device illustrative of certain constructional features of the invention, with various portions show-n in section; and

Figure 3 is a graphical presentation of representative characteristic response .curves achieved by the operation, as explained, of the electron'discharge device presented in Figures 1 and 2 'as illustrative of the present invention.

Referring now to the figures of'the drawing in further detail, the electron discharge device shown in Figures 1 and 2 comprises an evacuated envelope 10 enclosing an oxide-coated electron emissive cathode 11 of conventional elongated construction, which cathode 11 is preferably indirectlyheatedby a suitable'conventional heating element 12, through heater lead-in wires 13. Substantially co-extensive with the longitudinal dimensions of cathodell, andoutwardly arranged with respect thereto in the order named are a control grid 14 mounted on suitable supporting .rods 15, a screen grid 16 mounted on suitable supporting rods 17, and 'a space charge electrode 18 mounted onvsuitable supporting rods 19. A high voltage anode .20 is provided in the embodiment illustrated in spaced relation with cathode 11, as by mounting on a suitable rod connector 21 which is in turn sealed in envelope '10 and electrically ronnected to top cap 22 in a manner'known to the art. Interposed between said cathode 11 and high voltage anode 20 is electrostatic shielding means comprising shield electrode 23, maintained at suitable low shielding potential, as by electrical connection with cathode 11, as indicated at 24, the constructional arrangement of this connection takingthe form,as illustrated in Figure'2,"of a supporting member 24' in turn electrically connected with a metal connecting and supporting plate 25, as indicated at 26, said metal plate 25 also being electrically connected with and supporting said cathode 11, as indicated at 27. The aforementioned connecting and supporting plate 25 may be provided with an additional supporting rod 28 for structural rigidity, as desired. The various supporting rods and electrical connectors 13, 15, 17, 19, 24 and 28 are embedded in a press 29 and the appropriate connections made with terminal prongs 30 extending from conventional insulating base 31 secured to the press end of envelope 10, all in a manner well known to the art.

Typical circuit connections for utilization of the type of grid-controlled vacuum tube taught by the present invention are schematically presented in Figure 1, wherein cathode 11 is maintained at a low potential, as by connection with ground, as indicated at 32. Control grid 14 is connected to a suitable signal input 33 through circuitry including such arrangement as desired for maintaining said control grid at the necessary average control potential, as schematically indicated at 33'. A space charge zone 34 is provided by interconnection 35 of screen grid 16 and space charge electrode 18 and further connection 36 of these space charge defining elements with a suitable relatively positive potential, indicated at 37 to be B plus. High voltage anode 20 is in turn connected to a high voltage source 38 through a suitable load 39, across which the signal output 40 is developed.

It will be seen that by arrangement and connection of the electrode system as shown in Figures 1 and 2, the flow of electrons emitted from cathode 11 will be drawn into space charge zone 34 by the relatively positive potentials on screen grid 16 and space charge electrode 18. As the electrons enter space charge zone 34, they emerge from the electrostatic shield provided by shielding electrode 23 and screen grid 16 and become susceptible of attraction by high voltage anode 20 and in large measure will follow a path of travel to anode 20 through the unrestricted, open communication provided between the space charge electrode 18 and the outward extremities of shielding electrode 23, such electron path of travel being schematically indicated at 41. It will be discerned that operation of the electrode system of the invention may oftentimes result in some degree of electron flow to both screen grid 16 and space charge electrode 18, depending upon the relative potential thereof with respect to cathode 11 and anode 20. However, the signal current primarily utilized by the invention is that represented by the electron flow from cathode 11 to anode 20 in the manner set forth, although it is also contemplated that in certain applications the instant electrode system may also incorporate a variable or signal potential at screen grid 16 or space charge electrode 18, or both, to provide a degree of mixing or modulation of the basic electron current flow of the system.

It will be understood that high anode voltages appearing on anode 20 will cause substantial secondary emission of ions by high velocity electron bombardment, which ions would, in vacuum tubes of conventional design, in turn bombard and adversely affect the operation and effective life of oxide-coated cathode 11. By the electron system arrangement of the present invention, ions evolving by secondary emission from anode 20 are in large proportion collected by shielding electrode 23, as indicated at 42, with the remaining ions possibly deleterious to the cathode 11 traversing a trajectory 43 in the space charge zone 34 defined by equipotential screen and space charge electrodes 16 and 18. Even in certain circuit arrangements where it is found advantageous to maintain screen grid 16 and space charge electrode 18 at different potentials, as by connection of screen grid 16 with a B plus potential and by connection of space charge electrode 18 with a lower order potential such as ground, or vice versa, it will be found that because of the heavier weight of the ions entering the space charge zone, as indicated at 43, and because of the relatively small potential difference between screen grid 16 and space charge electrode 18, the ions in this zone will be deflected only slightly and will traverse the space charge zone as before or be collected either by the space charge electrode 18 or the grid Wires of screen grid 16 because of the relatively small angle of incidence with respect thereto.

Figure 3 graphically presents representative characteristic response curves, illustrating operation of an electrode system and associated control circuit embodying the principles of the present invention, wherein a positive B plus potential of 75 volts was applied to screen grid 16 and space charge electrode 18, the anode load 39 was 22 megohms, the anode high voltage 38 was varied up to 30 kilovolts, and selected control grid 14 voltages of 0, 1, 2, 3, -4, and 5 volts were successively established as the control potential applied to control grid 14. Anode spacing between anode 20 and shield electrode 23 was inch. At 5 volts grid potential, the electrode system exhibited no plate current, i. e. grid control cutoff condition, at an anode voltage up to 30 kilovolts. The resulting characteristic response curves presented in Figure 3 clearly illustrate an important feature of the present invention in that, at practical operating grid voltages in the range of -4 to 1 volts, further increase of anode voltage above 3 to 8 kilovolts, respectively, resulted in substantially no increase in anode current.

It has been demonstrated that considerable variation in the relative potentials maintained on the respective electrodes of the instant system may be adopted without departing from the scope of the invention, in that either of the electrodes 16 and 18 defining the space charge zone 34 may be operated at substantially equipotential with cathode 11. It will be further apparent that the potential maintained at shielding electrode 23 may be subject to some variation without departing from the scope of the invention. Thus, shielding electrode 23 need not be connected to cathode 11, as indicated at 24, but may alternatively perform the desired shielding function within the scope of the invention by connection with another source of relatively low potential. It is also to be discerned that the relative spacing between anode 20 and shield electrode 23 will directly affect the plate voltage rating of the tube, a spacing of inch having been shown to be adequate for anode voltage up to 30 kilovolts by way of example. Similarly, the anode current value is inversely affected by the spacing of anode 20 from the space charge zone 34 and directly affected by providing a space charge electrode of relatively greater diameter and/or higher screen grid and space charge electrode potentials. In addition, it will be self-evident that additional electron pervious grid electrodes may be interposed between cathode 11 and space charge electrode 18 in order to modify the flow of electrons from cathode 11 into space charge zone 34 by expedients known to the art per se, such as by a virtual cathode, additional screen or suppressor grids, or the like.

It will be further readily apparent to those skilled in the art that only a typical form of the invention has been illustrated and discussed and that various further modifications may be made in the disclosed electrode system and associated circuitry without departing from the basic features of the invention.

What is claimed is:

1. An electron discharge device comprising an envelope, and within said envelope a cathode, a control grid adjacent said cathode, electrostatic means surrounding and in substantially co-extensive relation with said control grid and said cathode establishing a positive field relative to said cathode to attract the electrons from said cathode and through said control grid to a zone adjacent thereto, an anode positioned to attract said electrons from the zone adjacent said electrostatic means and shielding means interposed between said anode and said cathode to prevent a direct electron flow therebetween.

2. An electron discharge device comprising an envelope, and within said envelope an elongated electron emissive cathode susceptible to contamination by ion bombardment, a control grid substantially co-eXtensive with and surrounding the longitudinal dimension of said cathode, electrostatic means surrounding and in substantially co-eXtensive relation with said control grid and said cathode establishing a positive field relativeto said cathode to attractthe electronsto a zone adjacent thereto, an anode positioned ,toattract the electrons from said zone, and shielding means-interposed between said anode and the adjacent end of said cathode to prevent the direct passage of electrons between said anode and said cathode, said shielding means being of lesser. compass transversely of said cathode than said anode.

3. An electron space discharge device comprising an envelope and within said envelope an electron emissive cathode having in surrounding relation therewith a control grid, a screen grid and a space charge electrode each arranged outwardly from said cathode in the order named to define a space charge zoneof a positive potential relative to said cathode between said screen grid and said space charge electrode, a'high voltage. anode in spaced relation with. said cathode, and an electrostatic shield interposed between said cathode and a portion of said anode to militate against the passage of. anode emitted ions to said cathode.

4. An electron space discharge device of the vacuum tube type capable of operation under highanode voltage conditions, comprising an evacuated envelope and within said envelope on elongate electron emissive cathode, a control gridin the discharge path from said cathode, a screengrid in surrounding and substantially co-extcnsive relation with said control grid, aspace charge electrode in surrounding and substantially co-extensive relation with said screen grid producing a space charge zone defined therebetween having a positive field with respect to said cathode, a high voltage anode in spaced relation with said cathode, and electrostatic shield means interposed between said cathode and the anode portion most adjacent thereto to prevent direct passage of the electrons from the cathode to the anode, and passage of ions from the anode to the cathode.

5. An electron space discharge vacuum tube of high anode voltage rating, comprising an evacuated envelope and within said envelope an elongate oxide coated cathode having, in effective surrounding relation therewith, a control grid, a screen grid spaced from and circumferentially about said control grid, a space charge electrode spaced from and circumferentially about said screen grid producing a space charge zone for attracting electrons from said cathode defined interiorly by said screen grid and exteriorly by said space charge electrode, a high voltage anode for attracting the electrons from said zone arranged in spaced and transverse relation with respect to one end of said cathode and having an efiective transverse dimension substantially co-extensive with said space charge electrode, and an electrostatic shield interposed between said end of the cathode and the adjacent anode portion to prevent direct passage of the electrons from the cathode to the anode, and passage of ions from the anode to the cathode.

6. An electron space discharge device of the vacuum tube type capable of operation under high anode voltage conditions, comprising an evacuated envelope and within said envelope an elongate electron emissive cathode susceptible to contamination by ion bombardment and in the electron discharge path from said cathode a control grid, a screen grid in surrounding and substantially co-extensive relation with said control grid, a

space charge electrode in surrounding and substantially co-extensive relation, with said screen gridproducing a space charge zone defined interiorly by said screen grid and eXteriorly by said space discharge electrode, a high voltage anode spaced from one end of said cathode, and electrostatic shield means interposed between said end of said cathodeand said anode to prevent direct passage of theelectrons from said cathode to said anode, and passage of ions from the anode to the cathode.

7. In an electronic control circuit, a grid controlled electron discharge vacuum tube comprising a low potential electron emissive cathode having in effective surrounding relation therewith a control grid, signalinput means connectedto' said control grid, a screen grid and a space charge electrode arranged in surrounding relation with said cathode'and said control grid, means for connecting to said screen grid and said space charge electrode a relatively positive potential with respect to said cathode, a high voltage anode in spaced relation with respect to said cathode, means for connecting a high voltage, to said anode, an electrostaticshield means interposed between said cathode andv a portion of said anode, and means-for connecting fa potential of a low order to said shield and ,to said cathode.

8. In a high voltage electronic control circuit, a gridcontrolled electron discharge vacuum tube comprising a low potential elongate oxide-coated cathode, a control grid spaced from and substantially co-extensive-with the longitudinal dimension of said cathode, signal input circuit means connected to said control grid, a screen grid and a space chargeelectrode arranged in surrounding and substantially co-extensive. relation with said cathode producing a space charge zone defined interiorly by said screen grid and exteriorly by said space charge electrode, said'space charge electrode being maintained at a relatively positive potential with respect to said cathode, a high voltage anode spaced from one end of said cathode and having a transverse dimension substantially coextensive with saidspace charge electrode, an electrostatic shield interposed between said endof said cathode and a portion of said anode, and means for connecting a low order potential with respect to said anode to, said shield.

9. A grid controlled vacuum tube capable of operation under high anode voltage conditions and exhibiting sharp grid control characteristics substantially independent of anode voltage, comprising an evacuated envelope and within said envelope an electron emissive cathode, a control grid, a screen grid spaced from and in surrounding relation with respect to said control grid, a space charge electrode space from and in surrounding relation with respect to said screen grid producing a space charge zone defined interiorly by said screen grid and exteriorly by said space charge electrode, a high voltage anode spaced from said cathode in open communication with the space charge zone, and electrostatic shield means interposed between said cathode and the portion of said anode most adjacent thereto.

10. A grid controlled vacuum tube having a high anode voltage rating and exhibiting uniform grid control characteristics substantially independent of anode voltage, comprising an evacuated envelope and within said envelope an elongate electron emissive cathode having in effective surrounding and substantially co-extensive relation therewith a control grid, a screen grid spaced from and in surrounding relation with said control grid, a space charge electrode spaced from and in surrounding relation with respect to said screen grid producing a space charge zone defined by said screen grid and said space charge electrode, a high voltage anode in spaced and transverse relation with respect to one end of said cathode having a transverse dimension in open communication with the space charge zone, and an electrostatic shield having a transverse dimension substantially co-extensive with said screen grid interposed between said end of the 7 cathode and the portion of said anode adjacent said end of the cathode. I

' 11. An electron discharge device including an envelope and disposed within said envelope a cathode susceptible of contamination by ion bombardment, a control grid surrounding said cathode, an anode spaced from said cathode, shielding means interposed between said cathode and said anode for protecting said cathode from bombardment by ions emitted from the area of said anode adjacent said cathode while permitting electrons to flow from said cathode to said anode, and electrostatic means spaced from and disposed circumferentially about said control grid and said cathode producing a relatively positive field about said control grid and said cathode to attract the electrons from said cathode to a zone which lies beyond the limits of said shielding means and in a direct path with said anode.

12. In an electron space discharge device, an electron emissive source, an anode, shield means interposed between said anode and said source to prevent the direct passage of electrons from said source to said anode, and means for establishing an indirect electron path between said source and said anode comprising electrostatic means for establishing a positive charge zone which is co-extensive with at least a part of said anode source to effect direct attraction of the electrons to said zone thereby, said electrostatic means being positioned to establish said zone beyond the limits of said shield, as projected, and in a direct path with said anode, to thereby permit attraction of the electrons from said zone by said anode.

13. In an electron space discharge device, an electron emissive source, an anode, shield means interposed between said anode and said source to prevent a direct flow of electrons therebetween, and means for establishing an indirect electron flow path between said anode and said source comprising an electrostatic means disposed adjacent said source to permit attraction of the electrons from said source to a zone adjacent thereto along a path which is blocked from said anode by said shield means, and means for supporting said anode in direct communication with said zone adjacent said electrostatic means to permit attraction of the electrons from said zone into impingement therewith.

14. In an electron space discharge device, an electron emissive source, including means for coupling a relatively low value potential thereto, an anode including means for coupling a relatively high potential thereto, shield means interposed between said anode and said source to prevent a direct flow of electrons therebetween, and means for establishing an indirect electron flow path between said anode and said source comprising an electrostatic means including means for coupling a relatively low potential thereto of a value sufficiently positive to said emissive source to effect attraction of the electrons from said source to a zone adjacent thereto, the electron flow between said source and said zone being blocked from said anode by said shield, and means for supporting said anode in direct communication with said zone to permit attraction of the electrons from said zone into impingement therewith.

15. In an electron space discharge device, an electron emissive source, an anode, shield means interposed between said anode and said source to prevent a direct fiow of electrons therebetween and to collect anode-emitted ions, and trap means for collecting anode emitted ions which escape said shield comprising at least a pair of electrostatic means, at least one of which is electron pervious, disposed in relative spaced relation adjacent said source to permit attraction of the electrons from said source into said trap over a path which is blocked from said anode by said shield, and means for supporting said trap forming electrostatic means in direct communication With said anode to permit attraction of the electrons from said zone into impingement therewith, and collection of the anode-emitted ions which escape said shield in said trap.

References Cited in the file of this patent UNITED STATES PATENTS 1,967,513 Ponte July 24, 1934 2,136,105 Jobst Nov. 8, 1938 2,190,079 Meier Feb. 13, 1940 2,314,916 Alma et al. Mar. 30, 1943 2,515,456 Loper July 18, 1950 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,864,027 December 9, 1958 William R. Aiken It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column '7, line 25, strike out "anode",

Signed and sealed this 10th day of March 1959.

SEAL) ttest:

KARL H, AQQLINE ROBERT C. WATSON Attesting Oflicer Commissioner of Patents 

